1. Field of the Invention
The present invention relates to the field of ureteral stents, and particularly to a stent having a novel distal curl which facilitates placement and removal of the stent within the kidney.
2. Description of the Prior Art
Indwelling ureteral catheter stents or drainage tubes have been used to bypass ureteral obstructions or ureteral-vaginal fistulas and maintain urinary drainage. In the past, stents made of straight lengths of open end tubing have been used for this purpose and have provided drainage for sustained periods of time. However, the use of such open end tubing has not been completely satisfactory. For example, in some instances the tubing has migrated and in others it has been expelled.
Various attempts have been made to produce stents which do not have the problems which accompany the use of such tubing. For example, stents have been designed which include an end flange to prevent migration of the stent. Another approach has been to provide the body of the stent with sharply pointed barbs which are designed to prevent migration and expulsion. However, such barbs increase the diameter of the stent, making it more difficult to insert and in some instances can cause the stent to migrate outside of the bladder. More recent stents have included a curve at one or both ends to prevent displacement.
Other important considerations with a ureteral stent are the ability to both accurately and conveniently place the stent, and readily remove the stent. These efforts will be significantly affected by the shape of the distal end of the stent. For example, hook-shaped or J-shaped kidney curls can present a problem when it is desired to remove the stent. The proximally-extending end of the curl can engage the interior of the kidney, such as in the area of the renal pelvis. Other prior art stents have been provided that include a full-circle or multiple curls. For these designs, it remains a factor that the shape of the distal curl may not be such as to prevent the tip from catching at the ureteropelvic junction. This can cause the stent to fold and kink in the ureter. Also, improper stent design can result in the stent being pulled into the ureter with the curl folded on itself.
In U.S. Pat. Nos. 4,212,304, issued July 15, 1979, and 4,307,723, issued on Dec. 29, 1981, there are disclosed ureteral stents which have hooks at each end which are provided for preventing migration and expulsion. Stents of this general type have been generally accepted because they can be easily introduced endoscopically and during open surgery. A ureteral stent having proximal and distal ends in the form of hooks and having open lumen at both ends is described in U.S. Pat. No. 4,610,657 issued to Densow on Sept. 9, 1986.
In U.S. Pat. No. 4,790,810 issued to Pugh, Jr., et al. on Dec. 13, 1988, there is disclosed a ureteral connector stent of adjustable length. The connector stent comprises an elongated, straight tubular member and a connector provided for coupling the tubular member with a curled end. As shown in the Pugh Patent, the curled end is generally in a helical shape, with the distal tip curling less than a full 360.degree..
Various stents having end curls have been made available in commercial embodiments. A ureteral stent sold under the mark UROPASS is available from Surgitek of Racine, Wis., and includes a kidney curl with the distal tip being positioned at a right angle to the stent body and extending a short distance across the body. Other prior art stents have included a pigtail curl at the distal end which has the distal tip formed in a 360.degree. curve. Still others have provided distal curls in excess of 360.degree., and ranging from approximately one and one quarter turns to as many as two or three full turns. Helical ureteral stents of these general types are disclosed in U.S. Pat. Nos. 4,531,933, issued to Norton, et al. on July 30, 1985, and 4,813,925, issued to Anderson, Jr., et al. on Mar. 21, 1989.
The present invention is based on the discovery that a particular kidney curl design satisfies the various needs for a ureteral stent in a manner not previously available. The novel curl design facilitates placement and removal of the stent to an extent not afforded by the prior art.